1. Field of the Invention
The present invention relates to methods for manufacturing hydrogen storage tanks and techniques for storing hydrogen within the hydrogen storage tank.
2. Description of the Related Art
Hydrogen is becoming more popular as an alternative fuel source and vehicles that utilize fuel cells as a source of power, instead of a combustion engine, have been proposed. Such fuel cells can efficiently generate energy by oxidizing hydrogen. Therefore, techniques have been proposed for effectively storing hydrogen using a hydrogen-absorbing alloy.
Known hydrogen-absorbing alloys absorb hydrogen when exposed to hydrogen under certain pressure and temperature conditions. By heating the hydrogen-absorbing alloy, hydrogen may then be released. Thus, in order to efficiently utilize a hydrogen-absorbing alloy to store hydrogen, the hydrogen-absorbing alloy must be activated to appropriately absorb and release hydrogen.
Pulverization has been described as one method for activating the hydrogen-absorbing alloy. By breaking up and pulverizing the hydrogen-absorbing alloy, a powdered hydrogen-absorbing alloy can be obtained. For example, Japanese Laid-open Patent Publication No. 7-157813 describes a technique of disposing a hydrogen-absorbing alloy within a vessel that is maintained in a vacuum or a hydrogen atmosphere. Then, shape memory alloy chips are disposed within or inserted into the hydrogen-absorbing alloy, thereby deforming the shape memory alloy chips. Due to the elastic restoring force of the shape memory alloy chips, the hydrogen-absorbing alloy will be broken up and pulverized by the shape memory alloy chips returning to their original shape.
However, when the hydrogen-absorbing alloy absorbs hydrogen, the hydrogen-absorbing alloy expands and the volume of the hydrogen absorbing alloy will increase. Therefore, the volume expansion ratio of the hydrogen-absorbing alloy during hydrogen absorption must be accurately calculated in advance in order to accurately determine the total amount of the hydrogen-absorbing alloy that will be filled within a hydrogen storage tank. Otherwise, excessively high stress will be exerted onto the hydrogen storage tank body due to the expansion of hydrogen-absorbing alloy that has absorbed hydrogen.
It is, therefore, an object of the present teachings to provide improved techniques for storing hydrogen.
In one representative method according to the present teachings, a hydrogen storage tank may be manufactured with a powdered hydrogen-absorbing alloy disposed therein. For example, an activation vessel first may be filled with a hydrogen-absorbing alloy. The alloy is preferably in a substantially solid block or ingot form. Then, hydrogen gas may be introduced into the activation vessel. The absorption of hydrogen gas preferably causes the hydrogen-absorbing alloy to pulverize and become substantially powdered. In other words, the hydrogen-absorbing alloy can be activated by absorbing hydrogen within the activation vessel. In a preferred embodiment of the present teachings, xe2x80x9cactivationxe2x80x9d may be defined by a process that enables the hydrogen-absorbing alloy to sufficiently absorb and store hydrogen. The term xe2x80x9csubstantially powderedxe2x80x9d is intended to encompass not only powders having a uniform diameter, but also a small pieces or chips of the hydrogen-absorbing alloy.
After activating the hydrogen-absorbing alloy in the activation vessel, a hydrogen storage tank can be prepared. For example, a vacuum may be applied to the hydrogen storage tank in order to substantially evacuate the interior of the hydrogen storage tank. In addition or in the alternative, a substantially inert gas may be introduced into the hydrogen storage tank. Thereafter, the interior of the hydrogen storage tank is placed in communication with (e.g., connected to) the activation vessel and the powdered hydrogen-absorbing alloy is transferred from the activation vessel to the hydrogen storage tank. According to the present teachings, accurate calculation of the volume expansion ratio of the hydrogen-absorbing alloy during the activation process and during the absorption of the hydrogen is not necessary, because the hydrogen-absorbing alloy has already expanded by absorbing hydrogen before being introduced into the hydrogen storage tank.
Other objects, features and advantage of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.